In food processing, foodstuffs can be pasteurized and/or sterilized to reduce the occurrence of food-borne diseases caused by harmful microorganisms. Pasteurization involves heating foodstuffs to a temperature, typically between 80° C. to 100° C., sufficient to kill certain pathogenic bacteria and microorganisms. In sterilization, foodstuffs are heated to a higher temperature, typically between 100° C. to 140° C., to ensure elimination of more resistant microorganisms. Sterilization allows normally perishable foodstuffs to be stored at room temperature for extended periods of time. Sterilized foodstuffs distributed for long-term preservation at room temperature are known as “shelf-stable” foods.
Traditional methods for pasteurizing and sterilizing foodstuffs involve the use of conventional heating processes (i.e., heating via the transfer of thermal energy from a high-temperature medium to a low-temperature substance), such as heating foodstuffs with hot air, hot water, or vapor. More recently, microwave heating has been employed for pasteurizing and sterilizing foodstuffs. Microwave heating is advantageous in that pasteurization and/or sterilization can be achieved in a much shorter time than is possible by conventional heating processes. By decreasing sterilization time, foodstuffs generally taste better and nutrient retention is improved. In addition, microwave systems typically are more energy-efficient than conventional heating systems.
However, attempts at commercializing microwave pasteurization and sterilization processes have had limited success. Some reasons for the lack of success in commercial operation are complexity, expense, non-uniformity of heating, and inability to ensure sterilization of the entire package. Thus, a need exists for new apparatus for pasteurizing and/or sterilizing foodstuffs, and methods for their use.